The present invention relates to feeders for feeding electronic components to automatic electronic assembly equipment.
Automated assembly apparatus have been known for some time that utilize robotic arms supporting pick up heads to pick up electronic components and automatically, rapidly and precisely position such components on a desired location on a printed circuit board (PCB) or a similar substrate. Such apparatus are generally known as pick and place systems.
Multiple xe2x80x9cfeedersxe2x80x9d are generally provided for use with a pick and place system, each for supplying one of the various electronic components that are to be placed on a particular substrate. The feeders are typically positioned parallel to each other on the horizontal table on the pick and place system. The feeders may be removed and replaced, such as to mount a new reel of carrier tape, or when changing over the configuration of a pick and place system to support a different printed circuit board requiring a different set of components. Alternatively, multiple feeders may be collectively mounted on a movable rack, and may be replaced en masse with a rack supporting a different group of feeders.
The electronic components are commonly located in individual pockets on a polymeric or paper strip called xe2x80x9ccarrier tapexe2x80x9d that is coiled on a supply reel rotatively supported on a feeder. The carrier tape includes sprocket holes on at least one longitudinal edge for advancing the carrier tape from the supply reel. Carrier tape also typically includes a removable cover tape that protects and secures the components within each pocket prior to use.
A feeder includes a mechanism to progressively advance the carrier tape to a pick up point to sequentially provide a single electronic component at a time for acquisition by a pick up head forming part of the pick and place system. The pick up head picks the component up and places it in position at a desired location on a printed circuit board. Most frequently, the pick up head includes a vacuum spindle that makes sealing contact with the electronic component to lift it up and carry it over to the substrate. Alternatively, mechanical grippers have been used to acquire an electronic component in place of a vacuum spindle.
The feeder progressively peels or cuts away the cover tape as the carrier tape is advanced to expose the electronic component to a pick and place head at the pick up point. Usually this is accomplished by detaching the leading end of the cover tape from the base tape. The free end of the cover tape is then engaged with and progressively pulled away from the base tape by a powered mechanism that maintains tension of the cover tape with a force greater than the adhesion force of the cover tape to the base tape. Typically, a stationary peeler overlies the cover tape adjacent to a pick up point and prevents the progressive detachment of the cover tape beyond the pick up point.
A movable shutter overlies the cover tape adjacent the peeler. The carrier tape is incrementally advanced to the pick up point by a separate powered mechanism, in response to a signal that the next incremental electronic component is needed by the pick up head. The carrier tape is advanced by a length sufficient to bring the next sequential individual electronic component to the pick up point. The shutter is then shifted in a direction to uncover the portion of the carrier tape that has been advanced with the single electronic component. Consequently, the portion of the carrier tape that has been advanced has its cover tape detached up to the peeler and removed by the powered mechanism. In some feeder designs, the shutter is eliminated entirely.
More recently pick and place systems have been devised that attempt to reduce the overall cycle time for populating a PCB with electronic components, by picking up multiple electronic components and then moving the group of components at the same time to the PCB for placement. These pick up heads include a plurality of vacuum spindles, each spindle to pick up a separate electronic component from one or more of the feeders. This approach recognizes that it is generally faster to pick multiple components and transport all of them as a group to the substrate to various desired locations, than it is to pick up, transport and place each electronic component separately.
However, this approach has encountered several difficulties that have limited its effectiveness. First, many pick up heads with multiple pick up spindles are capable of acquiring electronic components from a feeder at a rate faster than conventional feeders can advance each individual sequential electronic component of a particular type to a pick up point. This slows down the entire process while the pick up head is idle as the feeder is advancing.
The speed at which the feeder advances each sequential component is constrained by several factors. First, each time an electronic component is to be advanced, the entire mass of the supply reel and carrier tape wound thereupon and extending through the tape path must be accelerated, advanced and decelerated to a stop, all while the pick up head remains inactive and waiting for the component to arrive at the pick up point. Second, the electronic component within the pocket of the carrier tape is not secured therewithin, and therefore is not stable during this process. This requires additional waiting time at the pick up point for the electronic component to stabilize before the pick up spindle can acquire it reliably. Third, even if time is allowed for the electronic component to come to rest, the motion of detaching the cover tape and of moving the shutter may also introduce instability.
Finally, the electronic component may have an undesirable tendency to become stuck to the cover tape (such as by static electricity, moisture or surface energy) and removed from the pocket therewith or otherwise dislodged. All of these factors limit the degree to which the operation of conventional feeders may be accelerated.
An alternative approach would be to provide multiple feeders with the same component, so that the pick up head is able to acquire multiple units of the same electronic component by moving between multiple feeders as each feeder cycles forward after providing an electronic component. However, the linear space available for positioning feeders, and hence the number of feeders that may be utilized with a pick and place machine, is finite and limited for a given machine length. The complexity of components to be loaded on printed circuit boards is increasing, as is the number of components. In some cases, the size (width) of the components is also increasing. All of this places a premium on placement and maximum utilization of feeders, and increases the need to optimize the use of the feeders without limiting the speed that the pick up head operates at.
Thus, conventional feeders for pick and place machines, while having their own utility, do not adequately address the increasing speed of pick up heads relative to the speed at which the feeder advances each sequential individual electronic component into the pick up location.
The present invention provides a feeder for use with a pick and place machine having a pick up head with one or more pick up spindles. Each of the pick up spindles is for acquiring an electronic component from a pocket in a carrier tape with a base tape including a plurality of pockets, each for receipt of an electronic component. The carrier further includes a detachable cover tape over the electronic components in the pockets.
The feeder includes a housing having a longitudinal axis and an end proximate the pick up head and an opposing distal end, and a tape path extending therethrough for conveying the carrier tape to a pick up zone. The pick up zone being adapted to receive a length of the carrier tape with a plurality of electronic components therewithin for simultaneous presentation to the pick up head. Means are mounted on the housing adapted for advancing the carrier tape through the tape path to the pick up zone so that a plurality of the electronic components are simultaneously located within the pick up zone.
Means mounted on the housing adapted to incrementally remove the cover tape of the carrier tape in the pick up zone while the carrier tape is stationary to enable sequential acquisition of each uncovered electronic component in the pick up zone by one of the spindles of the pick up head.
In another embodiment of the present invention, two feeder mechanisms as described herein are mounted on the same housing, but operate independently of each other with two different carrier tapes.
The present invention further provides a method for providing electronic components seriatim supplied on a carrier tape having a base tape with a plurality of pockets, each for receipt of one of the electronic components, and a detachable cover tape for securing into a pick up zone for acquisition by a pick up head having one or more pick up spindles. The method of the present invention includes the steps of:
a) advancing the carrier tape along a tape path so that a plurality of electronic components are stationary and located within the pick up zone;
b) detaching and removing the cover tape over the pocket containing the leading component without moving the carrier tape;
c) lowering the first pick up spindle to acquire and remove the leading electronic component from its pocket;
d) detaching and removing the cover tape over the pocket containing the next sequential component without moving the carrier tape;
e) lowering the next pick up spindle to acquire and remove the exposed electronic component from its pocket; and
f) repeating steps d) through e) to remove all of the electronic components located in the pick up zone in step a).
The method further includes the additional step of repeating steps a) through f) above to maintain a continuous supply of a plurality of the electronic components in the pick up zone.